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<html lang="en">

  <head>
    <meta charset="UTF-8">
    <title>07_面试题2</title>
  </head>

  <body>

    <script type="text/javascript">
      function fun(n, o) {
        console.log(o)
        return {
          fun: function (m) {
            return fun(m, n)
          }
        }
      }
      var a = fun(0)
      a.fun(1)
      a.fun(2)
      a.fun(3) //undefined,

      var b = fun(0).fun(1).fun(2).fun(3) //undefined,

      var c = fun(0).fun(1)
      c.fun(2)
      c.fun(3) //undefined,
    </script>
  </body>

</html>